Herpes simplex virus associated rhomboencephalitis mimicking demyelination: a case report

Herpes simplex virus (HSV) is an uncommon but important cause of brainstem rhomboencephalitis, especially in immunocompetent individuals. Its presentation can mimic demyelinating disorders such myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), and neuromyelitis optica spectrum disorder (NMOSD), posing a diagnostic challenge.

We report a case of a 31-year-old previously healthy male who presented with holocranial headache followed by bilateral limb and facial numbness, right hemibody sensory loss, left temporal visual field deficit, and unsteadiness while walking. Neurological examination revealed dissociated sensory loss, gaze-evoked nystagmus, and impairment of cranial nerve functions, including visual field deficit and facial sensory loss, indicating involvement of the optic and trigeminal nerves, respectively. MRI showed hyperintensities in the pontine tegmentum and middle cerebellar peduncles with enhancement of bilateral trigeminal nerves. CSF analysis revealed lymphocytic pleocytosis. MOG and AQP4 antibodies were negative. VEP showed left optic pathway involvement. Initial treatment with intravenous methylprednisolone showed no improvement. A viral etiology was considered, and CSF PCR was positive for HSV. The patient improved significantly following a 21-day course of intravenous acyclovir.

This case underscores the importance of considering HSV rhomboencephalitis in the differential diagnosis of brainstem syndromes, particularly those mimicking demyelination. Early identification and antiviral therapy are crucial to prevent long-term neurological sequelae.